This invention relates to the inhibition of interactions of PDZ domains of a protein or proteins with other proteins, and more particularly to novel compounds that have been found to be effective in inhibiting PDZ domains. In a very specific aspect, this invention relates to the inhibition of a PDZ domain of proteins that regulate the function of the oncosuppressive protein PTEN, or of the PDZ domain of the Dishevelled protein (Dvl), and compounds that have been found to possess such inhibiting capability. Compounds of the invention have been shown to produce apoptosis in cancer cells overexpressing Dvl.
PDZ domains are regions of signaling proteins that function to modulate protein-protein interactions such as protein-protein recognition. PDZ domains were named for three proteins in which this domain was initially discovered: PSD-95 (a 95 kDa protein involved in the signaling at the post-synaptic density), DLG [Drosophila lethal(1)discs large-1], and ZO-1 (the zonula occludens-1 protein involved in maintenance of epithelial polarity). These proteins play important roles in neuronal synaptic transmission, tumor suppression, and cell junction formation, respectively. They are understood as functioning in vivo by organizing multiprotein complexes that function in signaling, e.g. communication between cells. For example, PDZ-organized signaling complexes are known to function in communication involving neurons or epithelial cells, e.g., by coupling activated receptors to downstream second messenger systems, and in transporting and targeting proteins to sites of cellular signaling. They are involved in the functioning of important cell signal mediators including ion channels, transmembrane receptors, and regulatory enzymes. PDZ-containing proteins are believed to be involved in disorders associated with defective cell signaling, including ischemic nerve damage and tumorigenesis.
Structurally, PDZ domains are 80-90 amino acid modular protein interaction domains that comprise six beta-strands (betaA to betaF) and two alpha-helices, A and B, compactly arranged in a globular structure. Peptide binding of the ligand takes place in an elongated surface groove as an anti-parallel beta-strand interacts with the betaB strand and the B helix. The structure of PDZ domains allows binding to a free carboxylate group at the end of a peptide through a carboxylate-binding loop between the betaA and betaB strands.
Among proteins with PDZ domains are the MAGIs (membrane associated guanylate kinase proteins with inverse orientation). Proteins in this class participate in the assembly of multiprotein complexes on the inner surface of the plasma membrane at regions of cell-cell contact. The MAGIs are a small family of adaptors, widely expressed in the human body, that have six PDZ domains. MAGI-3 binds to the tumor suppressor PTEN, a lipid/protein phosphatase, using its second PDZ domain (MAGI3-PDZ2). The interaction of MAGI-3 and PTEN decreases phosphotidylinositol 3-kinase and Akt/PKB signaling whereas release of PTEN from MAGI-3 increases Akt/PKB signaling. Normally, Akt/PKB signaling ensures cell survival during response to cellular insults by suppressing apoptosis. However, PTEN mutants that cause constitutive Akt/PKB signaling have been associated with human cancers. Chemical disruption of this interaction would be a unique way to investigate the role Akt/PKB signaling in transformation and cancer, and could affect the development of cancerous growths.
Also among proteins that have been found to possess a PDZ domain is the Dishevelled protein (Dvl). Its interactions with the Wnt and Frizzled proteins have been indicated as being involved in one or more types of cancers.
Small-molecule inhibitors of interactions of proteins having PDZ domains with other proteins would be desirable. Until recently, no small molecules having this capability were reported. In 2002 and 2003, we disclosed several compounds that had such a capability [Novak et al., Investigation of the PDZ Domain Ligand Binding Site Using Chemically Modified Peptides, Bioorganic & Medicinal Chemistry Lett. 2002 (2471); Fujii et al., Targeting PDZ-domain by Rationally Designed Non-peptide Small Molecules (poster) (American Society of Cell Biology, December 2002 meeting); Novak et al., Small molecule inhibition of a PDZ domain interaction (poster) (American Society of Biochemistry and Molecular Biology, April, 2003 meeting); Fujii et al., A selective irreversible inhibitor targeting a PDZ domain interaction protein, JACS 2003 125:12074.